The art is replete with mixing valves and control systems therefor of varying degrees of efficiency and complexity. Most such valves and controls depend upon outside sources of electrical power for their operation, require the presence of and close attention of operating personnel, and are only as efficient as is within the capabilities and skill of the personnel attending to their operation. The mixing valve and control system herein illustrated is designed to provide a combination of improvements in the construction and operation of mixing valves and the controls therefor which is not available in any known mixing valve, to wit, to provide a mixing valve which will be self-contained by employing one of the fluids to be mixed for controlling the system and to make operation of the system dependent on the presence of the other fluid; to provide for making adjustments at a location remote from the place of mixing so that the operator will not have to be present in the room where mixing is accomplished; to provide for varying the volume of flow and ratio of the fluids being mixed within the confines of a unit structure; to provide for making such changes while the system is in operation; and to provide a fail-safe system wherein the pressures of the fluids to be mixed must be at a predetermined set pressure before operation of the system can be initiated.